Beneficiating potash ores



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United States Patent ()fidce Patented June 5, 152-8?v 3,637,624BENEFKCIATWG PQTASH ORES Frank L. Jackson, Weston, (Iona, and Bernard M.Fisher and Gilbert L. Jordan, Carlsbad, N. Mex., assignors to NationalPotash Company, New York, N.Y., a corporation of Delaware Filed Aug. 20,1958, Ser. No. 756,174 2 Claims. (Cl. 209-4) This invention relates to anew and improved process for beneficiating potash ores and, moreparticularly, to a process for recovering from a sylvinite ore a sylviteconcentrate of desirable particle size which does not contain burdensomequantities of fines and is substantially free of dis-persible clay andother dispersible water-insoluble material.

Heretofore, beneficiation of sylvinite ores to recover potassic valueshas been generally limited to those ores which contain a relativelysmall percentage of dispersible clay, and other dispersible,water-insoluble material, i.e., about 3%, or less. However, as these oredeposits diminish, more eificient methods of processing ores having ahigher content of dispersible clay-like materials have been needed, buthave not been forthcoming. The major problems which arise in thebeneficiation of potash ores are usually attributed to thetransformation of these dispersible materials into slime form. It isgenerally believed that the dispersible clay constitutes a largepercentage of the slimes formed, and accordingly, the term dispersibleclay will be used hereinafter to mean dispersible clay and otherdispersible, water-insoluble material present in potash ores. Likewise,since the major beneficiation problems are associated with the amount ofclay present, the terms low-clay ore and high-clay ore are used hereinto refer to ores which respectively contain 3% or less of dispersibleclay and more than 3% of dispersible clay.

Several methods of processing low-clay ores have been employed torecover the sylvite concentrate therefrom. Customarily, these processesinclude the steps of wet grinding and classifying the ore, passing theground ore to a pulping tank, usually of the barrel type, where the oreis suspended in a brine solution saturated with respect to sylvite andhalite from which the ore is delivered to a hydro-separator where thecoarse sylvite and halite concentrate is separated from the clay andfines. The Wet grinding has been considered to contribute importantly tothe effective operation of the process. The concentrate obtained in thismanner is then processed in several steps including flotationseparation, where separation of sylvite and halite is effected.

Although this conventional type of processing has been foundsufliciently economical to be commercially acceptable for low-clay ores,it is not practical for the treatment of high-clay ores containing morethan about 3% of dispersible clay. As the clay in potash ore increases,various separation problems arise which cannot be overcome readily byadjustment of these customary methods of operation.

Among the disadvantages of known processes, especially when applied tohigh-clay potash ores, are the following:

Wet grinding produces a large percentage of fines making it desirable toprocess the fines separately to recover sylvite values, thereby addingto processing costs; the sylvite particles are excessively reduced insize during the processing, thereby reducing the market value of therecovered sylvite concentrate; insuflicient scouring action is providedto separate effectively the clay and particulate sylvite present in theore; unremoved clay impedes conventional flotation separation ofpotassium-containing concentrate and absorbs large quantities offlotation agent; and finally, known procedures for classifying anddesliming wet-ground high-clay ores are highly ineflicient.

It is an important object of this invention to provide an efficient anduncomplicated process for recovering a sylvite concentrate from bothhigh and low clay potash ores.

It is a special object of this invention to provide a method forproducing a mill feed, substantially free of dispersible clay, from ahigh-clay sylvinite ore without the production of an undesired quantityof fines.

It is another special object of this invention to provide a processwhereby a coarse sylvite concentrate can be derived from a high claysylvinite ore which permits a conventional flotation separation of KClin very high yields equivalent to and more, of the KCl content of theore.

Other objects and advantages of the invention will be apparent from themore detailed description of the invention which follows.

These and other objects of the invention are attained by: (1) Drygrinding all of the ore obtained from the mine, to a desirable particlesize, suitably, to a maximum of 10 mesh or preferably to about 12 or 14mesh, (2) Strenuously scrubbing the ground ore in an aqueous medium toseparate the clay from the sylvite particles and disperse it in theaqueous medium, and (3) Centrifugally separating the dispersed clay andother fines from the scrubbed ore particles to provide the sylvite oreconcentrate.

The invention can be readily understood from the important illustrativeembodiment, schematically represented on the accompanying flow sheet, asapplied to the continuous processing of a sylvinite ore. The ore treatedwas a sylvite-halite ore having the following analysis:

Dispersible clay and other dispersible water-insoluble materials 4.98Combined H O .61

The raw ore, as it came from the mine, was mostly inch mesh sizeand wasrun over a inch scalping screen to remove A1 inch ore particles. Thecoarser particle fraction was conveyed to a primary impactor crusher,and the minor fine particle fraction containing a major portion of theclay to an ore dryer and then to a 12 mesh screen. The crushed ore fromthe primary crusher was likewise conveyed to the 12 mesh screen. The +12mesh ore particles were conveyed to a secondary impact crusher and thecrushed ore reconveyed to the 12 mesh screen. The 12 mesh ore particleswere ready for the scrubbing treatment.

More particularly, it has been discovered that drying the fraction ofthe ore which contains the major portion of the clay and finessubstantially reduces blinding of the 12 or 14 mesh screens whichcontrol the particle size of the ore being processed. Although thelarger particles from the inch scalping screen make up the bulk of theore being processed, i.e., about of the ore, it has been discovered thatthis fraction, although later ground and screened contributes onlynegligibly to the blinding of the 12 or 14 mesh screens. Furthermore, ithas been discovered that while drying of the inch ore from the scalpingscreen considerably improves the efficiency of the 12 or 14 meshscreening of the ore, drying of the 4- /4 inch fraction or the recyclefrom the 12 or 14 mesh screens has not been found to be of anyadditional advantage. Rather, it has been found that drying thesefractions can be deleterious to the overall efficiencyof the process.The fact that the process operates very effectively by drying only afraction of the ore, results in important savings in equipment and fueland avoids excessive rises in the temperature of the brine and theresulting excessive dissolution of potash compounds which must berecovered by expensive recrystallization.

The crushers were operated continuously in closed circuit with thescreens. Intermediate screening and removal of undersize particles wasnot necessary. By adjusting the speed of the impactors to the properrate, recycling of the oversize material was controlled and overgrindingwas avoided. Through this control of the grinding operation, the productcontained a larger proportion of coarse particles, and as a result, thefinal purified ore product produced had a premium value in the market.

A typical sample of the crushed ore had the following particle sizedistribution, as determined by screening: l2 to +28 mesh, about 42.8%;28 to +100 mesh, about 40.7%; 100 to 200 mesh, about 9.7%; and less than200 mesh, about 6.8%. Only the material passing through the 200 meshscreen is considered fines, and analysis along the path of flow of theore showed that this material was rich in clay.

The dry crushed ore together with approximately an equal weight of anaqueous brine saturated with respect to potassium chloride and sodiumchloride were introduced continuously into the first compartment of acompartmented attrition scrubber. This brine was obtained from a laterstage of the process and was sufiicient only to provide a fluid mass ofhigh solids content. About 50% of brine, by weight, in the fluid masswas sufiicient. Each compartment of the scrubber was provided with ahigh speed impeller agitator. By operating the device at an adequatelyhigh speed, the particles were vigorously agitated, thereby forcing ahigh degree of inter-particle impingement at comparatively highvelocities and effecting strenuous scouring and scrubbing action on thegranular particles, which action removes clay without materiallyreducing grain sizes. This action also broke up cemented particles andexposed new surfaces, with the result that more effective scrubbing wasaccomplished. Unless the particulate KCl is scrubbed free of clay, theflotation reagents used for separating KCl from NaCl in the flotationcells, will not be effective.

The ore was underfiowed continuously from compartment to compartment inthe scrubber and was then flowed to a dilution tank suitably ofcylindrical shape. The number of compartments required in any particularoperation is determined by the tenacity with which the clay adheres tothe granular particles and the degree of scrubbing desired in this phaseof the process. The process can be accomplished in a single scrubbingcompartment, but, in this instance, not with an acceptable efficiency.

The mixture was maintained in the dilution tank in a continuous state ofhigh agitation by a stirrer and sui'iicient saturated brine was added toreduce the solids content of the liquor from about 50% to aboutAgitation may be facilitated by providing the dilution tank with fourbaflles mounted vertically and radially, equidistant around the wall ofthe tank.

The diluted pulp was then pumped continuously under pressure to ahydrocyclone separator where a first stage desliming was carried out.The diluted pulp was fed continuously and tangentially into the upperend of the elongated cyclone, clay and fines of relatively smallparticle size were removed axially and continuously as a stream ofrestricted diameter from the center of the upper end of the cyclonewhile a concentrate of the coarser ore particles was forced to the outerarea and removed continuously as a stream of restricted diameter fromthe lower end of the cyclone. The pressure used and the relative size ofthe outlets in the upper and lower part of the cyclone were adjusted toremove a coarse product having to solids from the bottom of the cycloneand to remove the remainder of the liquid containing the lower specificgravity fines and dispersed clay from the top of the cyclone. The brinewas recovered from the clay and fines in a slime leach system inconventional manner.

The partially purified coarse product obtained was next flowedcontinuously to a second scrubber provided with an impeller agitator.The brine containing the ore particles was vigorously agitated again toforce the particles to impinge upon one another and effect aninter-particle scouring action. While various types of scrubbers may beused, it was found, as in the first treatment, that a compartmentedscrubber obtained the greatest scouring action per unit of retentiontime.

After substantially all of the dispersible clay and other material to beremoved had been forced from the particles of ore, the suspension wasflowed continuously to a second agitated dilution tank where it Wasmixed with sufiicient fresh saturated brine to reduce its solids contentto about 17%. Then the resulting diluted suspension was pumpedcontinuously to a second centrifuge or hydrocyclone, where a major partof the brine containing substantially all of the remaining dispersibleclay and lines was separated from the coarse concentrate and returned tothe first dilution tank. The coarse efiluent contained less than 2% ofparticles of -200' mesh.

The granular sylvite ore concentrate, substantially free of all clay andfines, was passed to a conditioning tank Where flotation agents wereadded, then brine, in preparation for the flotation separation of thesylvite and halite in a known manner.

After the flotation separation and related crystallization, a coarsesylvite product was obtained containing KCl in a quantity at leastequaling a potassium oxide equivalent of 60.5%. In this way,approximately or more of the available KCl was recovered from the core.

In the illustrative embodiment of the invention specific details havebeen given with reference to procedures and apparatus, but it will beapparent the invention is not limited to these details. For instance,the impeller scrubbing of the ore body may take place in a singleattrition machine when a low-clay ore is used or the clay adheres to theore with less tenacity. Likewise, greater clay separation may beeffectuated by increasing the number of compartments. Also,hydrocyclones have proven especially advantageous for separating thescrubbed ore from the dispersed clay, fines, and other water insolublebut dispersible materials. However, other known types of centrifugalseparators may be used, somewhat less advantageously. In general, twoscrubbing steps and two centrifugal separatory steps are preferred whenhigh-clay ores beneficiated. Thus, it should be understood that thisinvention extends to all equivalent operations and apparatus which willoccur to those skilled in the art upon consideration of the principlesof the invention and the disclosed manner of practicing the invention.

What is claimed:

1. A method of beneficiating as-mined high-clay sylvinite ore containingat least about 3% of bound but waterdispersible clay, comprisingseparating the mined ore into (1) a major fraction of relatively largeparticles which upon subsequent dry grinding .do not tend to blind a 10mesh screen and (2) a minor fraction of relatively smaller particles ofa size and moisture content which normally tend to blind a 10 meshscreen, drying only said minor fraction of relatively smaller particles,subjecting said major fraction of relatively large particles to drygrinding, combining the resulting dried minor fraction and the resultingdry-ground major fraction and subjecting the resulting combineddry-ground major and the resulting dried minor fractions to a screeningtreatment on an about 10 mesh screen, feeding the particles of ore whichpass through said 10 mesh screen and an aqueous brine solution saturatedwith respect to potassium chloride and sodium chloride into a scrubbingzone to form a fluid aqueous mixture, said brine solution containingessentially only potassium chloride and sodium chloride, agitating themixture with such force that the ore is suspended in the brine and theore particles are forced into contact with one another at highvelocities and the clay is scrubbed from the ore particles and becomesdispersed and suspended in the brine, and centrifugally separating theparticulate ore from the dispersed clay and fines.

2. In the treatment of as-rnined potash ores containing at least about3% of bound but Water-dispersible clay to produce an ore concentrate,the steps comprising separating the mined ore into (1) a major fractionof relatively large particles which upon subsequent dry grinding do nottend to blind a mesh screen and (2) a minor fraction of relativelysmaller particles of a size and moisture content which normally tend toblind a 10 mesh screen, drying only said minor fraction of relativelysmaller particles, grinding the ore particles of said major fraction ofrelatively large particles to reduce the size thereof only by drygrinding, combining the resulting dried minor fraction and the resultingdry-ground major fraction and subjecting the resulting combineddry-ground major and the resulting dried minor fractions to a screeningtreatment on an about 10 mesh screen, feeding the particles of ore whichpass through said 10 mesh screen and an aqueous brine solution saturatedwith respect to potassium chloride and sodium chloride into a scrubbingzone to form a fluid aqueous mixture, said brine solution containingessentially only potassium chloride and sodium chloride, agitating themixture with such force that the ore is suspended in the brine and theore particles are 5 forced into contact with one another at highvelocities and the clay is scrubbed from the ore particles and becomesdispersed and suspended in the brine, and centrifugally separating theparticulate ore from the dispersed clay and fines.

References Cited in the file of this patent UNITED STATES PATENTS2,596,407 Jackson May 13, 1952 2,836,297 Smith et a1 May 27, 19582,846,068 Smith et a1. Aug. 5, 1958 2,950,007 Smith Aug. 23, 1960 OTHERREFERENCES Craiglow: Electric Heating of Screens, reprint from CeramicBulletin, 1950.

Rock Products, Lenhart, February 1952, pp. 100-103. ChemicalEngineering, Tangel, June 1955, volume 62, Number 66, pp. 234-238.Mining Engineering, Weems, August 1951, pp. 685-

1. A METHOD OF BENEFICIATING AS-MINED HIGH-CLAY SYLVINITE ORE CONTAININGAT LEAST ABOUT 3% OF BOUND BUT WATER DISPERSIBLE CLAY, COMPRISINGSEPARATING THE MINED ORE INTO (1) A MAJOR FRACTION OF RELATIVELY LARGEPARTICLES WHICH UPON SUBSEQUENT DRY GRINDING DO NOT TEND TO BLIND A 10MESH SCREEN AND (2) A MINOR FRACTION OF RELATIVELY SMALLER PARTICLES OFA SIZE AND MOISTURE CONTENT WHICH NORMALLY TEND TO BLIND A 10 MESHSCREEN, DRYING ONLY SAID MINOR FRACTION OF RELATIVELY SMALLER PARTICLES,SUBJECTING SAID MAJOR FRACTION OF RELATIVELY LARGE PARTICLES TO DRYGRINDING, COMBINING THE RESULTING DRIED MIONOR FRACTION AND THERESULTING DRY-GROUND MAJOR FRACTION SAND SUBJECTING THE RESULTINGCOMBINED DRY-GROUND MAJOR AND THE RESULTING DRIED MINOR FRACTIONS TO ASCREENING TREATMENT ON AN ABOUT 10 MESH SCREEN, FEEDING THE PARTICLES OFORE WHICH PASS THROUGH SAID 10 MESH SCREEN AND AN AQUEOUS BRINE SOLUTIONSATURATED WITH RESPECT TO POTASSIUM CHLORIDE AND SODIUM CHLORIDE INTO ASCRUBBING ZONE TO FORM A FLUID